Studying half-demons
by PEARLwolf67
Summary: Rin is being rejected by his friends because he is the son of Satan, but what will happen when Mephisto makes a surprise announcement?
1. announcement

**This Is my first time writing fanfiction so it may not be great, but I hope you stick around until the endJ.**

 **This fanfiction takes place after Rin's battle with Amaimon, but before Yukio became a demon.**

Rin Okumura sat at his desk trying to concentrate on the piles of homework Yukio had given him earlier that week. He had put it all off until Friday, which Rin was now deeply regretting.

"Damn that four eyes, he never lets me do anything fun!" Rin said to him right before the youngest of the Okumura twins came in through the door of the old dorm room. "Come on Nii-san you're going to be late for your classes again at this rate." Then after seeing the unfinished homework overflowing on his older brother's desk said "what _have_ you been doing all this time? You haven't done any of your homework at all!"

"Well…" Rin said while looking at his familiar Kuro chase a fly around the room for inspiration. He didn't want to tell Yukio what he was _really_ doing, Rin was pretty sure that he would disapprove of trying to cook vegetables with the flame that came from his tail. He couldn't help if he couldn't afford the expensive food at the school or that the power randomly shut off the most inconvenient times. "I was cooking…" he said not completely lying.

"For nine hours!?" yelled Yukio. Rin jumped at the sudden increase in his normally calm brother's voice, he looked down at his tail that had distracted him from his 'important' work, he was surprised to see that had fluffed up to about twice the size kind of like a cat's does when it is startled.

"Ok whatever, you can do it when you get back, but we really do need to hurry," Yukio said calming down a little. Rin responded with a long sigh, school had been like hell for the few weeks after his fight with Amaimon. None of his friends wanted to be anywhere near him after finding out that he was the son of Satan.

The twins grabbed their magical keys that they used to get to the cram school. Almost as soon as they went through the door they saw the group consisting of Shima, Izumo, Shiemi, Konekomaru, and Suguru "Good evening Okumura-sensei" they said to Yukio when they saw him.

Rin looked down the long hallway and saw twenty or thirty other cram school students standing outside of their assigned classrooms "what's happening?" he asked. Konekumaru looked at Rin like he was a six-foot tall spider that was about to eat him. Feeling hurt he turned to the others and asked the question again. "What the hell is happening!?"

"No one knows, all the doors are locked and no one can get in," Suguru said in an annoyed voice only to be knocked on his face by a familiar puff of pink smoke.

"My my, it seems that I have been careless and forgot to unlock the doors this morning" The students heard their principle Mephisto Pheles say as he stepped off of a rather angry Suguru. "Eins, Zwei, Drei," he said while waving his umbrella towards the locked doors which then magically flew open.

Rin walked into the old classroom that he and his friends used and sat down in the back, not wanting to have too much attention drawn to him today. After all of the students and a highly confused Yukio were seated. Mephisto made his announcement. "Ok class, and Mr. Okumura. I am going to give you all a group assignment that will be due on Monday, which includes you, Mr. Okumura.

"What the hell Mephisto!" yelled Rin completely failing at not being noticed "you are giving us an assignment over the weekend!?"

"If you prefer you can think of it as bonding time," Mephisto said amused. "What the hell is that supposed to mean ya' bastard?!" Rin yelled, his tail twitching from side to side.

"What I mean Rin Okumura… is that this class is going to by studying half-demons, in other words… you." 

**So it is 11 pm now and I am super tired, but anyway I hope you liked it I tried to put a bit of suspense there at the end. I will try to update it daily... maybe. Please tell me what you thought.**


	2. A Demonic Language

**Ugg, I regret staying up so late last night. Ok, so I start to call Suguro Bon in this chapter, not for any reason in particular. Thank you for the support and please enjoy the story :)**

Rin stood at his desk shocked, had he heard Mephisto correctly? He was giving the cram school class an assignment over the weekend and the assignment was to study him!? The young exwire did not like the sound of this, he sat back down in his chair feeling increasingly more uncomfortable as all of the students and Yukio turned to look at him almost questioningly.

"What is the meaning of this Mephisto" Yukio asked the principle who was apparently enjoying the confused faces of the students.

"To put it quite simply you are all going to be learning about the changes Rin's body made when he unlocked his demon powers." Mephisto said, and then he walked out twirling his umbrella and stopped in the doorway and said "I want you results by Monday" and then disappeared in a puff of pink smoke.

The group used their magic keys to leave the cram school and enter the Okumura's old almost empty dorm. "I am going to go get some materials for the experime… I mean the assignment" Yukio said leaving the room to go to the exorcist shop. He hoped that everyone could get along for at least 20 minutes.  
"This place gives me the creeps every time" Shima said shivering. Rin had a sudden wonderful idea "hey Shima," he whispered into the pink haired exwire's ear "I bet that the bugs that live here would love to meet you."  
Shima let out a scream loud enough to scare away any bugs that **did** want to befriend him. Bon heard Shima's scream and saw Rin standing next to his friend, "Get away from him demon!" he yelled.

"I wasn't doing anything Rooster!" Rin yelled not noticing that his tail was swinging back and forth behind him. "Who are you calling a rooster!?"Bon

"Isn't that obvious!?" Rin was so concentrated on his argument, that he hit a lamp of his still cluttered desk onto the floor with his tail.

"At least I don't have a tail that knocks over everything in a ten foot radius of me when I get angry!" Bon yelled making a very good point as most of Rin's week worth of homework was now on the floor.

Rin turned around and tried to grab his tail to stop it from its reign of destruction only to trip over a sleepy Kuro and fall next to Shiemi who was giggling at Rin's clumsy performance.

 **Rin are you ok, why did you bring these noisy people in here?** Rin heard Kuro's voice in his head like he always did. "Yeah Kuro I'm fine. Oh I forgot to tell you, but I made you dinner it should be in the kitchen" **I already ate it, it was yummy. Thank you.**

Yukio walked into the room. "Ok I'm back and I have everything we need" Yukio said. To tell the truth he had wanted test out his brother's demonic abilities before, but he couldn't figure how to ask Nii-san without it being awkward.

Rin looked around the room, Konekomaru was watching him carefully, Shiemi was petting Kuro, and everyone else was looking through the bag of things that Yukio had bought from the store.

Bon was the first to say anything about beginning the experiment "I think we should start by gluing that tail of his to the ground so that he doesn't hit any of us with it when we spray him with holy water."

"Holly water?" Rin said shaking a little bit "yeah I'm not a huge fan of that idea."

Izumo spoke up "I think we should start with his ability to speak demonic languages." Rin looked at her and was about to ask what she meant when Bon said "yeah a minute ago when he tripped over Kuro I thought I heard him speak a strange languge, but I wasn't sure."

Rin walked over to Konekomaru and sat down on the floor next to him "What about you Konekomaru you didn't hear me say anything strange did you?" the oldest Okumura said with a slightly worried look on his face.

"Well actually…" the bald exwire said as he was slowly moving back to his comfortable distance of seven feet from Rin.

"Nii-san, were you not aware that you spoke a different language when you speak to demons?" Yukio said looking up from cleaning the large mess that his brother's tail had made of the piles of paper and textbooks.

"What! You mean I have done this before!?" Rin's yelling startled Shiemi who was still petting Kuro and not paying any attention to the conversation in front of her.

The younger brother went back to his work and wrote something in an empty notebook he had found in the mess. "Yes you do it all the time I thought that you knew that you were doing it so I never mentioned it." He said with a much calmer tone than his brother's

"So are we going to actually get started or are we just going to keep talking about Rin's supidity all night?"

"Well, it's kinda late now so how about we start tomorrow?" Rin paused then a huge smile spread across his face "I can make you all dinner if you want, I just went shopping and I have enough ingredients to make a huge meal!"He said his tail wagging behind him obviously displaying his excitement.

"As if I would let _you_ cook me anything" Bon said standing up and leaving quickly.  
"What about the rest of you?" Rin said trying to hide his disappointment

"I w-would hate to have you waste your ingredients on me." Konekomaru said as he walked out of the room. Shima didn't say anything, but just followed Konekomaru out the door.

Rin now looked at Shiemi hopefully "Im sorry Rin my mother wants me to help in the shop early in the morning so I have to get home" she said truthfully.

"I can walk you home, my key to your house isn't working properly so I hope you don't mind walking." Yukio said as they walked out the door as the others had.

Rin wished that his friends would stop talking about him behind his back. He heard Bon say to Konekumuro and Shima "he thinks we can all just trust him all of a sudden just because we have to work together. Those blue flames he inherited from Satan can kill people!"

Rin laid on his bed silently cursing his demonic hearing then rolled onto his stomach after he accidently sat on his tail.

Outside of the Okumura's dorm Mephisto sat on a magically floating couch that was equally as bizarre as his clothing. "It seems that this assignment might be a little harder than Rin thought." He chuckled "I wonder if his friends will learn to except him or if he will continue to be an outcast in human society?"

 **This chapter was a lot longer than I expected, but I think it turned out well. Do you like the shorter or longer chapters. It is only 9 o'clock this time, I did start a lot earlier.**


	3. Don't touch my tail!

**Sorry for not posting a chapter yesterday, I had to go to the orthodontist. Braces suck. I am excited about this chapter so I hope you enjoy it!**

"Come on, we can't put this assignment off forever," Bon said to a very obviously stalling Konekomaru. "No, I can't leave yet! I have to… read my new book!" The exwire said reaching for a book about garden care that Shiemi had giving him for his birthday.

"Konekomaru you don't even like gardening, " Bon said dragging him out of the room and started walking to the old dorm building where the Okumura brothers lived.

"Wait! What If Rin gets angry? He might burn all of us!" Konekomaru yelled trying to escape Bon's grip. "Would you just shut up!?" Bon said as he opened the door to the Okumura's room.

"Ah… Okumura-kun…" the bald exwire said when he saw Rin standing at the door with a huge grin on his face. He looked around the room and was relieved to see that Shiemi, Izumo, and Shima were already there. He walked over to Shima and asked, "where is Mr. Okumura?"

"Yuki-chan is on a mission right now, he said we can do whatever we want as long as we stay inside of the building and if we keep notes on Rin'stail,." Shiemi said from across the room.

"So that's why you have been staring at me strangely since you came in. Its not like my tail does anything that interesting though." Rin said looking a little bit uncomfortable.

"That's not quite true Rin," Izumo said looking up from her notes "like for example did you know that when you get nervous or uncomfortable, like you are now, your tail wraps around your leg." Rin looked down, she was right his tail was tightly wound around his left leg. "And when you are angry all of the hair on your tail stands up." He was starting to get upset at the fact that he never noticed something as simple as that.

"That's not true!" Rin said angrily "hey why are you laughing!?"

"Rin look at your tail" Shiemi said trying to hold back her giggles.

He turned around, all the hair on his tail was standing up just like Izumo had said. "Ugg, not again!" Rin ran into the bathroom and came back out holding a comb. He sat down on his bed and started brushing his fluffed up tail.

This was too much, everyone in the room burst into laughter. Rin looked up slightly confused, "What?"

"Well, I never really imagined that you had to brush your tail..." Konekomaru said feeling a little bit more comfortable, Rin was kind of like a cat now that he thought about it.

"How else would I keep it clean?" Rin said, he had never really thought about it as strange before.

"Wait, don't tell me that you wash your tail in the shower every day too?" Shima said in a highly amused voice.

"No… why would I do that" Rin said hesitantly and then mumbled, "I wash it every other day."

"Ha, I knew it!" Shima said, "Izumo quick write this down, this is important information!"

"We are getting off track now, " Izumo said, "maybe we should test exactly how sensitive a half demon's tail is compared to a regular demon's tail." Rin definitely didn't like the sound of this "No you can't touch my tail!" he said as he ran behind Shiemi his tail narrowly avoiding Bon's hand. A few blue flames appeared around him and stuck his tongue out at his friends.

Bon looked at Rin with a slightly surprised look on his face, he wasn't expecting Rin to use his flames all of the sudden. Konekomaru moved towards the door in case he needed to make a quick retreat.

 **Ooo what's going to happen? Haha just kidding I know what's going to happen I'm the writer! This chapter was sooo much fun to write, I hope you enjoyed it as much as I did.**

 **Quick question, does anyone ever just completely forget to eat for like two days? No, just me, ok.**


	4. The Basement

_**Hey everyone,**_

 _ **I am so sorry for not updating in a few months. I hope this will make it up to you.**_

"Rin calm down!" Bon said looking around Shiemi who wasn't fazed by Rin's sudden burst of flames at all.

Konekomaru saw how close Bon and Shiemi had moved to Rin who still had blue flames all around him. "Bon, Shiemi move away from him, he might hurt you!"

Rin hearing this immediately put out his flames. His tail started to wrap around his waist, this was a habit that Rin had developed over the period of time that he had to hide his tail from the other exwires and basically everyone except for his brother and a few other people like Mephisto.

"Dam that clown!" Rin thought to himself, "things were already awkward between him and his friends, and Mephisto just _had_ to go and make everyone study him. What kind of assignment is that anyway!?"

A loud crash made Rin cover his ears, this was one of the times that he really hated his enhanced hearing. Even before his demonic powers had been unlocked he was very sensitive to loud noises and thunder storms were no exception.

"Well, it looks like we are going to be here for a while," Shima said looking out the window, the storm had come out of nowhere and it looked like it was going to last for a long time.

Izumo spoke up "just because there is a little storm doesn't mean we can't do our assignment. Here Bon take this bag and go catch a small goblin from outside. We will need a full demon to compare to Rin."

"No need. Yukio keeps different kinds of low-level demons in the basement. I was thinking we should go down there anyway, it's too loud up here and there is a kitchen down there." Rin said, half yelling, he was still covering his ears because of the loud thunder.

The group started down the stairs. Konekumaru started thinking to himself. Konekumaru was scared of him, but he was starting to question if he needed to be. Sure it would be a good idea to keep his guard up, but maybe he wasn't as scary as Konekumaru initially thought. Wait Rin was the spawn of Satan, he was to be avoided! What was he thinking! "Well if they are going to be testing him I guess I can tell if he is a danger or not."

"Here will this do, Izumo?" Rin asked waving his hand towards the 4 or 5 small cages lined up on the far wall. "Yes, this will do. I think this one will work." Izumo said looking into the biggest cage "This one is a relatively weak one but it should react about the same as you, Rin." The one she had picked looked like an overgrown rabbit. It had strange armor plate looking places, where there wasn't armor there was long pinkish-grey fur. Its tail was considerably longer than normal rabbits and it looked a bit like Rin's, but it was the same color of the rabbit demon's fur.

"So what are we going to do first?" Bon asked. He didn't want to admit it but he was interested in how everything was going to work, he had seen Rin's teeth, ears, tail, and he had seen him use his flames, but he had never asked about what it was like, what it was like to be a demon.

Izumo interrupted his thoughts "We should start with his tail to get it out of the way, just don't burn us in the process, ok Rin?"

" I don't have that little control over my flames!"

"Sure…"

"To start out with let's just write down some things that we notice his tail doing."

At Izumo's command, everyone began watching Rin's tail, which made him very uncomfortable. "Umm guys? Do you think that this could be a bit less, umm, strange?"

"Oh, I know! You can make us a snack!" Shima said, his stomach growling on cue.

"Hey! I thought that you didn't want anything!" Rin said. His tail started swishing back and forth again. Bon took out a piece of paper from his jacket pocket and wrote down something on the paper.

"Well that's before we were forced to stay here, but if we are stuck here we might as well have something to eat."

"Ok, I'll just cook some eggs or something "

Rin walked into the small basement kitchen and took out some ingredients. Everyone else sat down at the table and watched him as he cooked, or rather, watched his tail and took notes.

 _ **Have you ever noticed that two pages on Microsoft Word**_ is _ **like 1/2 of a page on here? Yeah, sorry for my short chapters. Talk to you all hopefully soon. Bye bye**_


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